DETERMINATION OF WESTERN PINE SHOOT BORER INCIDENCE, IMPACT, AND STAND HAZARD RATING CHARACTERISTICS IN SELECTED REGION ONE NATIONAL FORESTS

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2 DETERMINATION OF WESTERN PINE SHOOT BORER INCIDENCE, IMPACT, AND STAND HAZARD RATING CHARACTERISTICS IN SELECTED REGION ONE NATIONAL FORESTS by Allen S. Robertson Jerald E. Dewey Cooperative Forestry and Pest Management Region 1 P. O. Box 7669 Missoula, Montana 59807

3 I INTRODUCTION Increasing attention and investment are being directed towards intensive fiber and timber oriented forest management systems. Due to the increased costs associated with intensive management, any factors which significantly reduce projected value yields need to be identified and their effects evaluated. Ponderosa pine, Pinus ponderosa Laws., is a preferred host of the western pine shoot borer, Eucosma sonomana Kft., (Lepidoptera: Olethreutidae). This insect has been identified as causing substantial reduction in height growth and form of ponderosa pine in plantations 0 established in eastern Oregon (Stoszek 1973), Colorado, Arizona, New Mexico (Stevens and Jennings 1977), northern Idaho (Luther 1980), and central Idaho (Stoszek et al. 1981). Stoszek (1973) estimated that volume losses attributable to the shoot borer in eastern Oregon amounted to as much as 25 percent of the undamaged harvest volume. In central Idaho cumulative volume losses in 80 year old plantations of certain if) site and stand conditions were estimated to be as high as 13 percent (Stoszek et al. 1981). Aside from volume losses there is also a substantial value loss associated with reduction of form classes due to forking. Control measures for the shoot borer have been developed (Sower et al. 1979, Sartwell et al. 1980b, Overhulser et al. 1980). Thus, the need to identify plantations which are subject to high levels of shoot borer infestation and consequently high volume losses becomes apparent. Once "high risk" areas are identified managers will be,able to weigh the costs of controls against the costs associated with shoot borer losses. OBJECTIVES The objectives of this survey were: 1. To assess the incidence of shoot borer infestation in young ponderosa pine plantations in western Montana and northern Idaho. 2. To appraise the relationships between the incidence of shoot borer and the attributes of the plantation and develop a western pine shoot borer hazard rating system. 3. To assess the impact of shoot borer infestation on height growth of ponderosa pine plantations. METHODS Biology.--The western pine shoot borer, a native American moth, is found throughout the range of its principal host, ponderosa pine (Sartwell et al. 1980a). The adult moths emerge in early spring and lay eggs on the buds of their host. Egg hatching and larval activity begins at the start of shoot elongation in the spring. The larva bores directly into the pith region and feeds downward as the bud elongates. By midsummer the larva emerges from the shoot, drops to the ground and pupates in the duff, overwintering in this stage.

4 External symptoms of shoot borer infestation persist for several years after larval emergence and therefore supply information about recent infestation rates. These symptoms include: shortening of the needles and decreased spacing between stem units on the infested portion of the shoot; an approximately one-eighth inch emergence hole; swelling of the shoot in the vicinity of the emergence hole in years subsequent to the year of infestation; and a reduction in the terminal/lateral shoot ratio (Stoszek 1973). All ponderosa pine plantations in the 12- to 18-year age class in the western portion of Region 1 comprised the sample population. These plantations were stratified according to geographic region (northwestern Montana--Kootenai and Flathead National Forests; west-central Montana-- Lolo and Bitterroot National Forests; and northern Idaho--Clearwater and Panhandle National Forests). The Nezperce National Forest has previously been sampled for shoot borer by Robertson (1982) and Stoszek et al. (1981). Further stratification of sample plantations was based on vegetation series, i.e., ponderosa pine, Douglas-fir, grand fir, and subalpine fir (Daubenmire & Daubenmire 1968, Pfister et al. 1977), and elevational zone (3,000-4,500 ft; 4,600-5,500 ft; and 5,600-7,000 ft). From a total population of 300 plantations, 80 were selected for sampling. The number of plantations sampled within each stratum was proportional to the total number of plantations in that stratum. Within each plantation sampled, data on shoot borer infestaion rate and tree characteristics were collected using replicated systematic samples with random starts. Each of 10 samples consisted of a transect of two points at a 2-chain interval. The first point was 1 chain from the plantation boundary. Each transect lay perpendicular to the longest plantation boundary and started at a randomly selected distance along the boundary. At each point on the transect the nearest ponderosa pine was sampled for the following information: total height, height growth increment by year for 1978 through 1981, shoot borer infestation status of the terminal by year for 1978 through 1981, year of loss of terminal dominance, and indications of other damage. One of the two points on each transect served as the center for a 1/100-acre circular plot in which all trees (host and nonhost) were measured for height, diameter at breast height, and crown ratio. In addition the following information was collected for each plantation: elevation, physiography, slope, aspect, soil characteristics, geologic parent material, habitat type, method of planting, and site preparation technique. ANALYSIS Individual tree data was summarized to produce average growth rates, stocking densities, stand characteristics and shoot borer infestation rates for each plantation. Infestation rates for all plantations within a single sample stratum were used to calculate an average infestation rate and confidence interval for that stratum. Single variable regression models were developed (Nie 1975) to test the relationshps between individual site and stand characteristics and the incidence of shoot borer infested terminals. Stepwise regression was used to develop a multivariable hazard rating model for the prediction of shoot borer infestation rates in young ponderosa pine plantations.

5 All further data analysis was conducted on transformed infestation rate 41 data. The transformation used was: Infestation rate in radians = Arcsine -,percent infestation Any calculations using models in this report will yield infestation rates in radians. An estimate of the equivalent percent infestation rate can be made using the following formula: Percent infestation = 100 [Sine (radians)21 Impact.--A method similar to Stoszek's (1973) and Stoszek et al. (1981) was used to calculate height growth reduction due to shoot borer. Twelve of the total population of plantations were used for impact 10 assessment. These were equally divided between the following average percent infestation rate classes: 5-10 percent, percent, and percent. Each ponderosa pine internode length ( ) was grouped into one of four infestation categories: UU - Uninfested internode originating from a previously uninfested internode. 0 UI - Uninfested internode originating from a previously infested internode. IU - Infested internode originating from a previously uninfested internode. II - Infested internode originating from a previously infested internode. Only trees in which the longest internode was in the UU infestation 10 category were used for further analysis under the assumption that the uninfested internodes expressed a tree's "true" potential growth rate. Each of the infested internodes was compared with the uninfested internode from the same tree to calculate a growth rate reduction due to shoot borer infestation. Percent growth reduction for an internode was calculated using the following equation: 1 - length of infested shoot length of uninfested shoot x 100 = percent height growth reduction An average height growth reduction was calculated for each of the infested categories (IU, UI, II). The percentage of each infestation 40 category found in each infestation rate class was calculated. From this information the total shoot borer caused height growth reduction for a plantation was estimated. AP 0

6 RESULTS Strata Means.--Strata means and 95 percent confidence intervals are presented for each of the sample strata: geographic region (table 1), elevational zone (table 2), vegetation series (table 3). In addition, the same information is presented for each of the six National Forest samples (table 4). From table 1 it can be seen that west-central Montana has a significantly lower shoot borer infestation rate than the other two geographical regions. Elevational zone also contributes significantly to differences in infestation rates (table 2). Plantations at low elevations generally have higher infestation rates than those at high elevations. Table 1.--Mean shoot borer infestation rate (percent) and 95 percent confidence intervals for each geographical region. West-central Montana--Bitterroot NF & Lolo NF 7.14 percent n = 49 Northwestern Montana--Kootenai NF & Flathead NF percent n = 23 Northern Idaho--Panhandle NF & Clearwater NF percent n = 8 Table 2.--Mean shoot borer infestation rate (percent) and 95 percent confidence intervals for each elevational zone. 3,000-4,500 ft percent n = 41 4,600-5,500 ft percent n = 24 5,600-7,000 ft percent n = 15 Table 3 shows a significant difference between infestation rates in various vegetation series; Douglas-fir and subalpine fir series showing the lowest infestation rates and the grand fir series exhibiting the highest rates. The differences seen between infestation rates in each Forest (table 4) can largely be attributed to the Forest's mean eleva- 41 tion. The Kootenai National Forest, having the highest infestation rate, is primarily in the lowest elevational zone where high infestation rates are expected (table 2). In contrast, the Bitterroot National Forest, which is at a substantially higher elevation, has the lowest 41 infestation rate. 40

7 Table 3.--Mean shoot borer infestation rate (percent) and 95 percent confidence intervals for each vegetation series. Douglas-fir series 7.84 percent n = 52 Grand fir series percent n = 24 Subalpine fir series 7.50 percent Table 4.--Mean shoot borer infestation rate (percent) and 95 percent confidence intervals for each National Forest. Lolo National Forest 8.04 percent n = 21 Bitterroot National Forest 6.47 percent n = 28 Flathead National Forest 7.64 percent n = 9 i Kootenai National Forest percent n = 14 Clearwater National Forest percent n = 5 10 Idaho Panhandle National Forest 7.50 percent n = 3 5

8 Table 5 presents descriptive statistics for each of the plantations sampled. Table 5.--Descriptive plantation statistics. Stand Elevation Age Avg. height Ponderosa TPA 1 / Total TPA Ponderosa BA 2/ Total BA Percent infestation Lolo National Forest n Bitterroot National Forest

9 Table 5.--continued Stand Elevation Age Avg. height Ponderosa TPA 1/ Total TPA Ponderosa BA 2 / Total BA Percent infestation Flathead National Forest Kootenai National Forest Clearwater National Forest Idaho Panhandle National Forests / Trees per acre 2/ Basal area 7

10 Single Variable Regression Models.--The relationships between all single site and stand variables and the incidence of shoot borer infestations are presented in table 6. The average diameter of the ponderosa pine on a plantation appears to be, by far, the best single predictor of shoot borer infestation rate (R2 =.361). Other important variables are annual basal area growth rate (BA/AGE), (R2 =.342), basal area (R2 =.327), average annual height growth over the last 3 years (R2 =.320) and elevation of the plantation in 100's of feet (R 2 =.319). Table 6.--Linear regressions of single site and stand variables infestation rate. on Variable Equation 1-2 SSE Site Elevation X.319*.135 Plantation age X Slope X.103*.155 Ponderosa pine stocking Trees/acre X Basal area X.293*.138 % Trees/acre X % Basal area X Average d.b.h X.361*.131 Other species stocking Trees/acre X Basal area X.118*.154 Average d.b.h X All species stocking Trees/acre X Basal area X.327*.134 Average d.b.h X.295*.138 Ponderosa pine growth rate Height/age X.316* Height X.319*.135 Height growth X.320*.135 BA growth/age X.306*.136 BA growth/tpa/age X.283*.139 All species growth rate Basal area/age X.342*.133 Basal area/tpa/age X.238*.143 SSE - Standard Error of Estimate. * - Significant at 95 percent level. 8

11 Multivariable Regression Model.--The multiple variable relationships tested lead to the development of a model which accounted for 60 percent of the variation in shoot borer infestation rate. The model is expressed by the following equation: Y = X X X X2X3 where: Y = a plantation's average shoot borer infestation rate (in radians) X1 = number of ponderosa pine/acre X2 = plantation elevation (100's of feet) X3 = annual ponderosa pine basal area growth increment PPBA/PPTPA/AGE X2X3 = interaction term (X2*X3) R2 =.602 SEE =.106 Infestation rate mean =.2415 Impact.--Table 7 presents the estimated percent height growth reduction for a plantation at three shoot borer infestation rate classes. Growth reductions range from 5.00 percent at an infestation rate of 5-10 percent to percent at an infestation rate of percent. Table 7.--Height growth loss by infestation rate class and category. Percent of internodes in Internode Percent infestation category at Percent growth loss at infestation growth infestation rate of infestation rate of 5-10% 15-20% 25-30% 5-10% 15-20% 25-30% UU UI IU II Percent height growth reduction

12 APPLICATION OF THE MODEL A ponderosa pine plantation's risk to shoot borer can easily be calculated utilizing the model developed in this report. All of the data necessary for inclusion in the model are readily available or can be easily obtained. An example follows using data from Lolo National Forest stand number Xi = ponderosa TPA = 270 X2 = elevation = 41 (100's of ft) X3 = ponderosa BA/TPA/AGE = 17.1/270/18 =.0035 X2X3 =.0035 x 41 =.1443 y = X X X X2X3 y = infestation rate in radians To convert "infestation rate in radians" to "infestation rate percent" utilize the formula: In this example: 100 [sine (radians) 2 ] is infestation rate in radians; Convert to degrees ( /radian): (0.4146) ( ) = ; sine of = (0.4028) 2 = x 100 = 16.23% Infestation rate percent The calculated infestation rate (16.23 percent) is close to the actual infestation rate for this particular plantation (18.75 percent). This procedure may be used to acquire an estimated infestation rate for any ponderosa pine plantation for which the proper data have been collected. Shoot borer caused impact at this infestation rate can be estimated by using table 7. The infestation rate of percent is closest to the percent infestation rate class which has a percent height growth reduction of percent. Estimates of volume reduction may be made using local managed yield tables and the estimated height growth reduction for the plantation. Stoszek et al. (1981) established that shoot borer infestation rates remain fairly constant throughout a rotation beginning at year 10. Volume yields at rotation can be made with and without shoot borer height growth reduction to esimtate volume reduction. Estimates of volume reduction will be conservative since yield tables are derived from stands having some shoot borer activity. 10

13 a DISCUSSION This survey has produced a tool for the evaluation of shoot borer impact. The model developed for shoot borer infestation rate prediction is based on readily obtainable management information: elevation, stocking, and basal area growth increment. The model will be helpful to the manager in determining where shoot borer infestations may become a problem. These variables are not of a nature that allows for silvicultural manipulation. However, when linked with impact (growth reduction) projections, the hazard-predictive model can be used to reassess plantation yield projections utilizing local yield tables. From this, costs and benefits of alternative plantation management practices can be assessed. Once the manager has an idea of what values are being lost, he will then be able to determine what control measures (if any) are warranted. It is possible that on sites of high risk and high impact, application of mating disruptive synthetic sex attractants may be cost effective for reducing the infestation rate to acceptable levels (Sartwell et al. 1980b). Thinning a plantation to reduce the stocking of ponderosa pine would reduce the incidence of shoot borer but would also tend to be counter-productive. During the plantation establishment phase, nonhost species might be planted provided they are found to have higher growth potential than the shoot borer impacted ponderosa pine. Applicability of the model and impact estimates are limited to the strata from which the data were collected. This includes ponderosa pine plantations in western Montana and northern Idaho between the ages of 12 and 18 years, and 3,000-7,000 ft in elevation. Attempts to extrapolate this information to areas outside these strata may cause significant errors.

14 LITERATURE CITATIONS Daubenmire, R. J. and J. Daubenmire Forest vegetation of eastern Washington and northern Idaho. Wash. Agr. Exp. Sta. Tech. Bull No. 60, 104 pp. Luther, S. C Western pine-shoot borer infestation levels in ponderosa pine associated with site conditions. Univ. of ID, M.S. Thesis, 55 pp. Nie, N. H SPSS:Statistical package for the social sciences. McGraw Hill, 675 pp. Overhulser, D. L., G. E. Daterman, L. L. Sower, C. Sartwell, and T. W. Koerber Mating disruption with synthetic sex attractants controls damage by Eucosma sonomana (Lepidoptera: Tortricidae, Olethreutidae) in Pinus ponderosa plantations. II. Aerially applied hollow-fiber formulation. Can. Entomol. 112: Pfister, R. D., B. L. Kovalchic, S. F. Arno, and R. C. Presby Forest habitat types of Montana. USDA Forest Serv. Gen. Tech. Rept. INT-34, 174 pp. Robertson, A. S Shoot borer hazard rating system for ponderosa pine in central Idaho. Univ. of ID., M.S. Thesis, 66 pp. Sartwell, C., G. E. Daterman, T. W. Koerber, R. F. Stevens, and L. L. Sower. 1980a. Distribution and hosts of Eucosma sonomana in the western United States as determined by trapping with synthetic sex attractants. Ann. Entomol. Soc. Amer. 73: Sartwell, C., G. D. Daterman, L. L. Sower, D. L. Overhulser, and T. W. Koerber. 1980b. Mating disruption with synthetic sex attractants controls damage by Eucosma sonomana (Lepidoptera: Tortricidae, Olethreutidae) in Pinus ponderosa plantations. I. Manually applied polyvinyl chloride formulation. Can. Entomol. 112: Sower, L. L., G. D. Daterman, C. Sartwell, and H. T. Cory Attractants for the western pine shoot borer, Eucosma sonomana and Rhyacionia zozana determined by field screening. Environ. Entomol 8: S Stevens, R. E. and D. T. Jennings Western pine shoot borer: A threat to intensive management of ponderosa pine in the Rocky Mountain area and southwest. USDA Forest Serv. Gen. Tech. Rept. RM-45, 8 pp. 12

15 Stoszek, K. J Damage to ṗonderosa pine plantations by the western pineshoot borer. J. For. 71: Stoszek, K. J., A. S. Robertson, S. B. Laursen, and P. G. Mika Field Survey: Western pine-shoot borer on the Nezperce, Payette, and Boise National Forests. Final report to the USDA Forest Serv., Forest Pest Management, Region 4, Ogden, UT, 63 pp. 13